Electromagnetic relay



May s, 1962 Filed July l2, 1960 J. K. DEAN, J R

ELECTROMAGNETIC RELAY 2 Sheets-Sheet l SWITCH ARM N0.I

TERMINAL INVENTOR'l JOHN K. DEAN JR.,

BW MMM ST ATTORNEY.

May 8, 1962 J. K. DEAN, .JR 3,033,957

ELEOTROMAGNETIC RELAY Filed July 12, 1960 2 Sheets-Sheet 2 OPEN CLOSED OPEN CONTACT No.4 CONTACT No.4 CONTACT NO. 3 FIGA y l f 56 e l swlTCH ARM No4@ @/'wlTcH ARM No.3

so suPPORI J SUPPORT No.4 C No.3

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SUPPORT 48 NO.|

SWITCH ARM NO.I 5o

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OPE'N CLO'sED \OPEN CONTACT NO.| CONTACT No.2 CONTACT No.2

lNvENToRi.v JOHN K. DEAN JR.J l

BM ATTORNEY.

56 SUPPORT NO2 3,033,957 Patented May 8, 1962 3,033,957 ELECTRGMAGNETIQ RELAY John K. Dean, lr., Lynchburg, Va., assigner to General Electric Company, a corporation of New York Filed .Iuly 12, 1969, Ser. No. 42,263 6 Claims. (Cl. 20G-104) The invention relates to an electromagnetic relay, and particularly to an electromagnetic four-pole double-throw relay that may have relatively small dimensions.

In the electronic and related industries, the present trend is to miniaturize the apparatus as much as practically possible. However, despite such miniaturization, the electrical and mechanical demands on the apparatus remain the same, or even increase, with respect to the demands on previous relatively large apparatus. Consequently, an effort is presently being made to miniaturize such apparatus and at the same time provide such apparatus with increased capability and durability. However, a limitation on the ability to miniaturize may exist because of the frequent requirement that the apparatus be capable of handlingy an appreciable current and voltage. In the case of electromagnetic relays, while miniaturization has been achieved with relays capable of handling several amperes of current, it is believed that it has not been possible to accomplish this with relays having more than two poles.

Accordingly, it is an object of the invention Ito provide a novel electromagnetic four-pole double-throw relay having an arrangement of parts so that it can be constructed to have relatively small physical dimensions.

Another object of the invention is to provide a relatively small electromagnetic four-pole double-throw relay that is rugged, and that is capable of switching and carrying appreciable amounts of electrical current.

These and other objects are accomplished in accordance with the invention by an electromagnetic relay which, briefly, comprises an elongated Core about which is wound a coil. rl`he core and coil are mounted in a frame supported by and above a base. Between the frame and the base are loca-ted at least four movable switch arms each having two associated fixed contacts. The switch arms and their contacts are mounted on terminals supported by the base and have their free ends located centrally above the base in the same general area. An L-shaped armature is pivoted about a point or axis at a lower corner of the frame. The armature is provided with an actuator which, when the armature is operated in response to encrgization of the coil, serves to move all four of the free ends of the switch arms between their respective contacts.

The invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the claims. In the drawing:

FlGURE l shows a side elevation view, partly in section, of a preferred embodiment of an electromagnetic relay in accordance with the invention;

FIGURE 2 shows an end elevation view of the electromagnetic relay of FIGURE 1;

FIGURE 3 shows a perspective View of the armature and its actuator; and

FIGURE 4k shows a plan view of the base of the relay of FIGURE l and the location of the terminals and arrangement of certain contacts.

In the figures, the same reference numerals refer to the same parts. With reference to FIGURES 1 and 2, there are shown side and end elevation Views respectively of an electromagnetic relay in accordance with the invention. The relay comprises a base or header 1d which may be formed of a magnetic material having a flat upper surface and a recessed lower surface as shown. The base 10 is preferably rectangular in shape and serves to support the relay structure and also serves to support external contacts. A cover 12, shown in cross section, may be provided and suitably fastened to the base 10 in order that the relay may be hermetically sealed. A frame 14 made of a suitable magnetic material is mounted above the base 1t). The frame 14 may be formed from a flat sheet which is cut and shaped to provide a three sided,

generally U-shaped, structure when viewed from above.`

The frame 11i includes two long sides 16 which extend along the length of the base 10, and which are generally parallel to each other and to the long sides of the base 10 and which lie in planes perpendicular to the upper surface of the base lil. The two long sides 16 are joined at one end by a short side 1S which lies in a plane perpendicular to the two long sides 16 and to the upper surface of the base lll. The frame 14 is supported by and fastened to the upper surface of the base 1G by four legs or supports 2li, these legs 2d being cut (out of the frame material if desired) and first bent inward and then downward so that they extend downward from the frame 14 some distance in from the edges of the vbase 10 as shown more clearly in FIGURE 2. The legs 20 may be welded to the base le. The two long sides 16 of the frame 14 are suitably notched near their center and at the lower edge to provide adjustable stops 22. The function of these stops 22 will be explained in detail hereinafter. The two long sides 16 of the frame 14 are also provided with suitable openings 24 for receiving and holding a retainer spring as will also be explained in detail hereinafter. An elongated cylindrically shaped core 26 of magnetic material is positioned between the two long sides 16 of the frame 14 and is fastened at one end to the central portion of the inner surface of the short side 1S. This core 26 extends for the length of the two long sides 16 of the frame 14. The free end of the core 26 and the free ends of the long sides 1 of the frame 14 preferably lie and terminate in a common plane as seen in FIGURE l. A coil spool or form 2S made of a suitable material such asV plastic is wound with an operating coil 3) which is comprised of a suitable number of turns or windings brought out on leads 31. rilie coil form Zd and its coil 30 are dimensioned so that they can pass over or around the core 26 and between the free or open ends of two long sides 16 of the frame 14. The vertical surfaces of the free ends of the long sides 16 of the frame 14 may be provided with notches 29 to receive a support (not shown) of non-magnetic material which is positioned in the notches 29 and fastened to the long sides 16 and to the `free end of the core 26 to provide additional strength to the relay structure.

The magnetic circuit of the relay in accordance with the invention comprises an armature 32 which may be generally described as being L-shaped. lIn addition to being shown in FIGURES 1 and 2, the L-shaped armature 32 is shown in the perspective View of FIGURE 3. The armature 32 comprises a rst or actuator arm 34 and a second or magnetic operating arm 36. These arms 34, 36 are comprised of flat sheet-like magnetic material, and lie in respective planes which meet at an angle to form a corner. As shown in FIGURE 1 the interior angle so formed is approximately but not necessarily 102 degrees. The actuator arm 34 of the armature 32 is, as shown in FIGURE 3, generally T-shaped, and includes a crosspiece 35 which is provided to restrict movement of the armature 32 in the upward direction of movement by engaging or striking the stops 22 of the frame 14. The crosspiece 35 also serves as means for fastening an actuator 4t) thereto. The actuator 40 is made of a flat strip of insulating material such as ceramic or plastic and is provided with a longitudinal slot 41 and a transverse opening 42`which permit the actuator 40 to be slipped upward from beneath the crosspiece 35 and fastened thereto by suitable means such as cement. Attaching the actuator 40 from beneath is desirable as it serves to place the actuator 40 in compression (which can be easily withstood) when the relay is operated. Thus, the actuator arm 34 of the armature 32 is provided with an actuator 40 which moves in accordance with movement of the armature 32 but which is electrically insulated from the armature 32. The magnetic operating arm 36 of the armature 32 may be generally rectangular in shape and is provided with a Vrounded portion 37 and two tabs 38.'V The'two tabs 3S lie in substantially the same 'plane a'sthe actuator arm 34. As shown in FIG- URE 1, the armature 32 is positioned with the actuator arm 34 between the frame 14 and the upper surface of the base 10, and with the magnetic operating arm 36 in the vicinity of the free ends of the two long sides 16 of the frame 14 and in the vicinity of the free end of the core 26. The pivot point or axis of the armature 32 is provided by the interior or inside corners of the angle formed by the two tabs 38 and the magnetic operating arm 36 of the armature 32 which rest against the corner formed generally by the lower portions of the free ends of the long sides 16 of the frame 14, and formed specifically by the portions of the legs 20 which are bent inward from the free ends of the long sides 16 of the frame 14. The armature 32 is normally retained in the position shown in FIGURE 1 (that is with the ends of the crosspiece 35 resting against the stops 22) by means of a retainer spring 44. 'Ihe retainer spring 44 is formed of a suitable wire and is given a shape which, in one sense, may be described as being W-shaped as will be seen in FIGURE 2. The free ends of the W-shaped configuration are bent to tit into the retainer spring openings 24 in the long sides 16 of the frame 14, and the central apex of the W-shaped contigurationris bent to rest in a depression 46 positioned on or near the exterior portion of the corner of the armature 32 formed by the magnetic operating arm 36 and the actuator arm 34. The retainer spring 44 is so shaped and biased that it urges the armature 32 to normally take the position shown in FIGURE l.

The magnetic flux path for the electromagnetic relay of the invention includes the core 26, the short side 18 of the frame 14, the two long sides 16 of the frame 14, the magnetic operating arm 36 of the armature 32, and finally the air gap between the magnetic operating arm 36 and between the free ends of the core 26 and the long sides 16 of the frame 14. When the coil 30 i-s energized, the magnetic flux produced thereby draws the magnetic operating arm 36 to the left as viewed in FIGURE 1 toward the free ends of the core 26 and the two long sides 16. This movement causes the armature 32 to rotate in a counterclockwise direction about its pivot axis until the magnetic Operating arm 36 rests against the free ends or as closely as possible thereto, of the core 26 and the long sides 16. When the armature 32 is so rotated, it will be seen that the actuator 40 and the crosspiece 35 of the actuator arm 34 are moved downward or in a counterclockwise direction about the pivot axis of the armature 32. This movement of the crosspiece 35 and the actuator arm 34 is utilized to effect switching of the contacts in the electromagnetic relay. v

The location of external terminals 48 for the relay contacts, for the switch arms, and for the coil terminals are shown inthe plan view of FIGURE 4 in addition to being shown in FIGURES 1 and 2. The external terminals 48 extend through the base 10 and are insulated therefrom by means of suitable insulators i) which may E be glass or other suitable material that holds the terminals 48 in a strong insulated relationship with respect to the base 10. FIGURE 1 shows a cross sectional view of one of the terminals 48 and its insulator 50. The terminal designations (i.e., the relay elements to which they are connected) are given in the figures. In FIGURE 4, it will be seen that the terminals 48 are laid out in a grid pattern or arrangement in three rows along the long dimension of the base 1th The relay shown comprises four switch arms S2 which are formed from a ilat strip of resilient material having good electrical conductivity such as an alloy of silver, magnesium, and nickel. The switch arms 52 are fastened by means of brackets 54 to their respective terminals 48 which are located at both ends of the two outer rows (i.e., at the corners of the base 10). The switch arms 52 extend inward in directions substantially parallel to the long sides of the base 10 and to the long sides 16 of the frame 14 to ward the central area of the base 10 between the base 10 and the frame 14. As shown in FIGURE 2, the `switch arms 52 are outside of the legs 20 of the frame 14. The free ends of the switch arms 52 terminate in the vicinity of the actuator 40 of the armature 32 so as to be operated in response to the downward motion of the actuator 40. When the armature 32 is in its normal position as shown in FIGURE 1, the switch arms 52 are spaced from the actuator 40, the crosspiece 35, and the actuator arm 34. Associated withY each switch arm 52 is a normally closed contact 56 positioned above the free end of the switch arm 52 and fastened to support terminals 60 which are located near the center of the base 10 and held by the insulators 50. The additional sup port terminals 60 for the normally closed contacts 56 are not essential, but may be provided to make the relay more rugged. The support terminals 60 do not extend beneath the lower surface of the base 10 for external connection as they are provided only as support for the normally closed contacts 56. The normally closed contacts 56 are shaped and bent as shown in the figures so as to be fastened to their respective external terminals 48. FIGURE 4 shows particularly how each of the normally closed contacts 56 is connected to a support terminal 60 as well as to an external terminal 48 so as to provide external connections for the normally closed contacts 56. Also associated with each switch arm 52 is a normally open contact 58 positioned below the free end of the switch arm 52. The normally open contacts 58 are fastened directly to their external terminals 48 in the two outer rows. The coil leads 31 are attached to their external terminals 43 in the center row. The normally open contacts 58 are shown in FIGURE 1, and since they do not have a peculiar configuration, they do not need the additional support provided for the normally closed contacts 56.

The switch arms 52 are biased or arranged so that their free ends normally tend to bend upward away from the base 1t) to engage or contact their respective normally closed contacts 56 as shown. When the relay coil 30 is energized, however, the armature 32 pivots in a counterclockwise direction about its pivot point or axis and the actuator 49 on the actuator arm 34 moves downward and strikes the free ends of the four switch arms 52 and moves the switch arms 52 downward until they break contact with their respective normally closed contacts 56 and make contact with their respective normally open contacts 58. The counterclockwise movement of the armature 32 is restricted by the magnetic operating arm 36 striking or contacting the free ends of the long sides 16 of the frame 14 and the magnetic core 26. As persons skilled in the relay art will appreciate, some slight additional travel is provided after the switch arms 52 contact the normally open contacts 58 to insure good contact and some wiping action. The actuator 40 will hold the switch arms 52 in the position just described as long as the coil 30 is energized. When the coil 30 is no longer energized, the bias provided by the retainer spring 44 and the switch arms 52 causes the armature 32 to pivot in a clockwise direction about its pivot axis and thus permits the switch arms 52 to move upward and break contact with their respective normally open contacts 58 and make contact with their respective normally closed contacts 56 once again, Some wiping action is desirable in this operation also. The clockwise movement of the armature 32 is restricted by the crosspiece 35 which strikes the stops 22. on the long sides 16 of the frame 14.

Persons skilled in the relay art, particularly such persons engaged in relay manufacturing, will appreciate the advantages offered by a relay in accordance with the invention. In the manufacture of a relay in accordance with the invention, the location and attachment ot the normally closed and normally open contacts associated with all four switch arms may be made before the attachment of the frame and its associated parts to the ba-se. The frame, when attached to the base, forms a rigid assembly. The free end or face of the core may be ground before the coil and form are placed on the core and the armature is placed in position. The armature may be pre-formed to the correct dimension relative to the core and the free ends of the switch arms which move between the eight stationary contacts. The actuator may be relatively small and light since, when operated, it is subjected only to compressive forces which are easily withstood by refractory ceramic materials. The free ends of the four switch arms are grouped together near the center area of the relay so that the single, small light actuator may move them simultaneously and directly such that the forces on each switch arm remain balanced one against the other. The armature pivot axis is located substantially at the same vertical level and perpendicular to the motion of the four switch arms so that the wear from sliding between the actuator and the switch arms is a minimum. The armature may be arranged so that the actuator pushes the switch arms at a point removed from the contact itself, thus providing an action which is conservative in its utilization of force and motion from the coil and core. This type of action is elective in lessening contact bounce both on pickup and dropout functions of the relay. vThe stationary contacts may be made from composite contact and base metal which may be punched from at stock and formed into a domed contact. The contacts may be trimmed to the desired length subsequent to their attachment to the base and subsequent to positioning and adjustment of normally closed contact pressure. The arrangement of the contacts and switch arms around the perimeter of the base and the horizontal orientation of the contact gaps both make the contacts and switch arms easily accessible for adjustment, cleaning, and inspection. The configuration of the base permits a small area to carry 14 terminals on a small grid spacing which is symmetrical and reversible in a plug-in socket and which requires no polarization of the terminals. The small number of different parts, the independence in manufacturing tolerances, the squence of manufacturing operations, the multiplicity of functions performed by each part, and the arrangement of the parts all combine to make an improved relay.

The relay described above has been successfully built and operated with an embodiment of small dimensions.

For example, a relay having the four switch arms shownA was built with dimensions which were approximately 1.0 inch long, 0.8 inch high, and 0.6` inch wide. The terminals were spaced 0.2 inch in each direction from each other. This relay provided contacts and switch arms capable of switching two amperes at 28 volts direct current. Further, this relay was extremely rugged, and operated after being subjected to shock in the order of 50 Gs of magnitude. Thus, it will -be seen that the relay meets the needs and desires for miniaturized equipment and, at the same time, provides a relay capable of switch- 6 ing an appreciable amount of electrical current. While the invention has been described with reference to a particular embodiment, it is to be understood that modiiications may be made by persons skilled in the art without departing from the spirit of the invention or from the scope of the claims.

What I claim as new desire to secure by Letters Patent ofthe United States is:

l. An electromagnetic relay comprising a base, a frame mounted on and above said base, a core of magnetic material mounted on said frame, a coil wound onsaid core, a generally L-shaped armature of magnetic material cornprising la -frst arm and a second arm which meet at an angle to form a corner, said armature being positioned 'with said rst arm between said frame and said base, with said second arlm in the vicinity of said core, and with an interior portion of said corner contacting a corner of said frame to pivot thereabout, an armature retainer comprising a generally W-shaped elongated element having its outer ends fastened to said frame and having its inner vertex contacting an exterior portion of said corner of said ar-mature to cause said interior portion of said corner of said armature to bear against said corner of said frame, a movable switch arm mounted at each corner of said base and generally extending toward the centr-al portion of said base between said base and said coil and frame, said switch arms being positioned with relation to said first arm of said armature so as to be moved in response to movement of said armature, and contacts associated with each of said switch arms.

2. An electromagnetic relay comprising a base, a frame mounted on and above said base, a core of magnetic material mounted on said frame, a coil wound on said core, a generally L-shaped armature of magnetic material comprising a trst arm and a second arm which meet at an angle to form a corner, said armature being positioned with said iirst arm between said frame and said base and with said second arm in the vicinity of said core, means pivotally mounting said armature adjacent a corner of said frame, said mounting means including an element that engages and supports said armature at substantially a point on said corner, a plurality of movable switch arms mounted adjacent the ends of said base and generally extending toward the central portion of said base between said base and said coil and frame, means carried by said rst Iarm of said armature and engageable 'with said switch arms, and contacts associated with each of said switch arms.

3. An electromagnetic relay comprising a rectangular base, la frame mounted on and above said base, a core of magnetic material mounted on said frame, a coil wound on said core, a generally L-shaped armature of magnetic material comprising a first arm and a second arm which meet at an angle to lform a corner, said armature being positioned with said rst arm between said frame and said base, with said second arm in the vicinity of said core, and with an interior portion of said corner contacting a portion of a corner of said frame to pivot thereabout, an armature retainer comprising a generally W-sh-aped elongated element having its outer ends fastened to said frame and having its inner vertex contacting an exterior portion of said corner of said armature to cause said interior portion of said corner of said armature to bear against said corner of said frame, a plurality of elongated movable switch iarms formed of a flat strip of material, means for fastening one end of each of said arms at a respective corner of said base with the other end of each of said arms extending toward the central portion of said base between said base and said coil and frame, said other ends of said switch arms being positioned in the vicinity of each other and near said rst arm of said armature so as to be -moved in response to movement of said armature, and contacts associated with each of said switch arms and positioned to be contacted by said switch arms in response to movement of said switch arms.

4. An electromagnetic relay comprising a rectangular base Ihaving a surface boun-ded by two parallel long sides and two parallel short sides, a U-shaped frame of magnetic material mounted on and above said base by legs, said frame comprising three sides lying in planes which are perpendicular to said surface of said base, two of said three sides of said frame being parallel to each other and to said long sides of saidv base and being joined at one end by the third of said three sides of said frame which is perpendicular to said two parallel sides of said frame, an elongated core of magnetic material positioned between and extending the length of said two parallel sides of said frame with one end of saidcore fastened to said third side of said frame, a coil wound on said core, an L-shaped armature of magnetic material comprising a first arm and a second arm which lie in respective planes that intersect at an angle to form a corner, said armature being positioned with said first arm located between said coil and said base, with said second arm located in the vicinity of the free end of said core, and with interior portions of said corner of said armature contacting exterior corners of the free ends of said two parallel sides of said frame and portions of two of said legs so as to pivot thereabout, a retainer comprising a generally W- shaped 'wire having its outer ends respectively fastened to said two parallel sides of said frame and having its inner vertex engaging an exterior portion of said corner of said armature to cause said interior portions of said corner of said armature to bear against said exterior corners of said two parallel sides of said frame and to cause said first arm of said armature to tend to bear against said coil and said two parallel sides of said frame and said leg portions when Said armature is in its normal position, said armature being operated by energization of said coil to cause said first arm of said armature to tend to move laway from said coil andr said two parallel sides of said iframe, a switch terminal located in the vicinity of each of the four corners of said base, a plurality of switch arms formed of elongated flat material, means fastening one end of each of said switch arms to a respective one of said switch terminals with said switch arms extending inward therefrom substantially parallel to said long sides of said base toward the center area of said base so that the free ends of said switch arms are located generally in the vicinity of the free end of said first arm of said armature, an actuator positioned on said -free end of said first arm. of said armature and arranged to contact each of said free ends of said switch arms and to operate said switch arms in response to movement of said armature, and a pair of contacts positioned in the vicinity of each of said free ends of each of said switch arms, said contacts being arranged above and below said switch arms respectively.

5. An electromagnetic relay comprising a rectangular base having a surface bounded by two parallel long sides and two parallel short sides, a U-shaped frame of magnetic material mounted on and above said base by legs, said frame comprising three sides lying in planes which are perpendicular to said surface of said'base, two of said three sides of said frame being parallel to each other and to said long sides of said base and being joined at one end by the third of said three sides of said frame which is perpendicular to said two parallel sides of said frame, an elongated core of magnetic material positioned between and extending the length of said two parallel sides of said frame with one end of said core fastened to said third side of said frame, a coil wound on said core, an L-shaped `armature of magnetic material comprising a first arm and a second arm which lie in respective planes that intersect at an angle to form a corner, said armature being positioned with said first arm located generally between said coil and said base, with said second arm located in the vicinity of the free end of said core, and with interior portions of said corner of said armature contacting portions of two of said legs near the free ends of said two parallel sides of said frame so as to pivot thereabout, means coupled to said long sides of said frame and engaging said armature to cause said armature to assume said pivot position and to pivot in response to energization and deenergization of said coil, a switch terminal located in the vicinity of each of the corners of said base, a plurality of switch arms formed of elongated fiat material, means fastening one end of each of said switch arms to a respective one of said switch terminals with said switch arms extending inward therefrom substantially parallel to said long sides of said base toward the center of said base so that the free ends of said switch arms are located generally in the vicinity of the free end of said first arm of said armature, an actuator positioned on said free end of said first arm of said armature and arranged to contact each of said free ends of said switch arms and to operate said switch arms in response to movement of said armature, and a pair of contacts positioned in the vicinity of each of said free ends of each of said switch arms, said contacts being arranged above and below said switch arms respectively.

6. An electromagnetic relay comprising a rectangular base having a surface, bounded by two parallel long sides and two parallel short sides, a U-shaped frame of magnetic material mounted on and above said base -by a plurality of legs, said yframe comprising three sides lying in planes which are perpendicular to said surface of said base, two of said three sides of said frame being parallel to each other and to said long sides of said base and being joined at one end by the third of said three sides of said `frame which is perpendicular to said two parallel sides of said frame, an elongated cylindrical core of magneticV material positioned between and extending the length of said two parallel sides of said frame with one end of said core fastened to said third side of said frame, a coil wound on said core, an L-shaped armature of magnetic material comprising a first arm including an actuator arm and tabs and a second arm, said first and second arms lying in respective planes that interesect at an angle to form a corner, said armature being positioned with said first arm located between said coil and said base, with said second arm located in the vicinity of the free end of said core, and with interior portions of said lcorner of said armature formed by said tabs of said first arm and by said second arm contacting portions of said legs in the vicinity of the free ends of said two parallel sides of said `frame so as to pivot about said leg portions, a retainer comprising a generally W-shaped wire having its outer ends respectively fastened to said two parallel sides of said -frame and having its inner v vertex engaging an exterior portion of said corner of said armature to cause, when said armature is in its normal position, said interior portions of said corner of said armature lto bear against said leg portions and to cause said first arm of said armature tol tend to bear against said coil and said two parallel sides of said frame, a switch arm terminal located in the vicinity of each of the four corners of said rectangular base, a plurality of switch arms formed of elongated at material, means fasteningone end of each of said switch arms to a respective one of said switch arm terminals with said switch arms extending inward therefrom substantially parallel to said long sides of said base toward the center area of said -base so that the free ends of said switch 'arms are located generally in the vicinity ofthe free end of said actuator arm of said armature, an actuator positioned on the yfree end of said lactuator arrn of said armature and arranged to contact each of said free ends of said switch arms and to operate said switch arms in response to movement of said armature, a normally closed contact positioned in the vicinity of each of said free ends of each of said switch arms between said switch arms and said frame, said normally closed contacts being arranged to contact their respective switch arms when said armature is in its normal position and to be spaced References Cited in the le of this patent UNITED STATES PATENTS Martin Nov. 17, 1959 Titus Dec. 22, 1959 Wallace Mar. 15, 1960 Alexandersson Dec. 20, 1960 Deissler Jan. 24, 1961 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3o33,957

May 8l, 1962 John K. Dean Jr.,

It is hereby hat error appea certified t ent requiring correction and rs in the above numbered patthat the said Letters Patent shouldread as corrected below.

Column 5V line 58, for "squence" read sequence column 8 line 2i, after "said" `-0 y first occurrencm insert- (SEAL) Attest:

ES'I'ON G. JOHNSON DAVID L. LADD Attesting Officer Commissioner of Patents 

